Click to download
Antioxidant therapy prevents endothelial cell senescence in a sub-group of atherosclerotic patients
In vascular endothelial cells (EC), telomere shortening, a consequence of somatic cell division, leads to a non-diving state called replicative senescence ( Allsop et al., 1995) . Telomere shortening is suggested also to occur in the presence of oxidative stress associated with risk factors for cardiovascular disease (CVD; von Zglinicki, 2002 ). Since premature replicative senescence of EC is associated with CVD, we hypothesized that a chronic treatment with an antioxidant could delay the apparition of senescence by decreasing oxidative stress and thus preserving telomere integrity. EC were isolated and cultured from human internal mammary artery discarded during coronary artery bypass graft surgery. Replicative senescence was induced in vitro by serial passages and quantified by a cytochemical detection of senescence-associated β-galactosidase (X-Gal) at pH 6. Telomere restriction fragment length (RFL, bp) was measured by southern blotting. To study the impact of an antioxidant on cell senescence, a group of EC was treated chronically with N-acetyl-L-cystein (NAC, 10µM). Reactive oxygen species (ROS) were quantified as a marker of oxidative stress. Nuclear expression of p53, telomerase (hTERT) and level of HNE, a marker of ROS-induced lipid peroxidation, were observed by immunofluorescence. Our data reveal 3 different groups of patients characterised by 3 responses to NAC: (1, n=4) beneficial, (2, n=5) intermediate or (3, n=4) no effect. In the first group, ROS and HNE decrease with NAC (P<0.05) as nuclear expression of p53 (P<0.05), whereas hTERT is translocated from the cytosol to the nucleus. Furthermore, while telomere length decreased in control EC (-23±6bp/day), RFL increased with NAC treatment (+25±14bp/day). Consequently, the apparition of senescence in non-treated EC (X-Gal50% = 108±16days) was prevented with chronic NAC treatment (P<0.05). In the intermediate group, telomere lengthening was transient in the presence of NAC (-11±2bp/day versus +1±6bp/day, P<0.05), whereas X-Gal was slightly delayed (X-Gal50% = 106±2days, P<0.05) when compared with control EC (X-Gal50% = 102±2days). Finally, in the third group, the antioxidant NAC had no effect. In conclusion, our results suggest that NAC could delay or prevent the apparition of cell senescence by preserving telomere integrity potentially by activating hTERT. This diversity of response to the antioxidant is probably due to the severity and/or the duration of exposure to oxidative stress associated with risk factors for cardiovascular disease.
Allsop et al. (1995). Exp. Cell. Res. 200, 194-220. |
